Preheat oven to 350°F. Grease, spray with cooking spray, or line a 10 x 15-inch jelly roll pan with parchment paper (see the notes below for a different size pan). Set aside.
PREPARE THE BARS
In a large bowl, use an electric mixer to combine the eggs, sugar, oil and pumpkin until smooth and completely combined; set aside.
In a separate bowl, whisk (or sift) together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, cloves, allspice and ginger.
Add the flour mixture to the pumpkin mixture; mix until combined. Mix in the vanilla extract. Spread batter in prepared pan. Bake for 20-25 minutes, or until toothpick inserted into center comes out clean. Cool completely in pan on wire rack.
PREPARE FROSTING
In a medium bowl, use an electric mixer to beat together cream cheese and butter until smooth. Gradually add powdered sugar and vanilla extract; beat until fluffy and smooth.
Spread on cooled bars. Dust with extra cinnamon, if desired.
Notes
Sheet Pan Pumpkin Bars: instead of a 15x10-inch jelly roll pan, you can bake the bars on a larger 13x18-inch rimmed baking sheet. The bars will be a bit thinner, so they will likely require a slightly shorter baking time. Start checking them at the 15-minute mark, and leave them in the oven until a toothpick inserted in the center comes out clean.
Pumpkin Bars Recipe in 9x13 Pan: instead of a 15x10-inch jelly roll pan, you can bake the bars in a smaller 9x13-inch baking pan. They will be slightly thicker, so they may require a couple of extra minutes in the oven.
No Frosting: of course, you can skip the cream cheese frosting if you like -- the bars will still be delicious! You might like to dust the tops with a little bit of powdered sugar or a dollop of whipped cream for presentation, but that's also optional.
Pumpkin Bars with Nuts: add a cup of chopped walnuts or pecans directly to the batter for some extra crunch, or garnish the top of the frosted bars with toasted nuts.
Raisins, dried cranberries, or chocolate chips would all be tasty additions to the flavorful batter.
I prefer a can of Libby’s 100% pure pumpkin, but you can substitute with 1 cup of fresh homemade pumpkin puree.
Make sure that you use a can of 100% pure pumpkin puree, which is different from canned pumpkin pie filling. The pure pumpkin puree is unsweetened and doesn't include any spices or other seasonings.
Use full-fat block-style cream cheese for the frosting. The cream cheese frosting will be thin and runny if you substitute with low fat cream cheese or cream cheese spread from a tub.
Sift the powdered sugar to avoid any lumps in your frosting.